The invention generally relates to fans for use in cooling systems. The invention relates particularly to a seal structure in a gap between the shroud and rotor of the fan to reduce noise by removing the swirling components of air flow at the tip region of fan blades and to minimize air leakage across the gap resulting in fan efficiency gains.
Conventionally, in axial flow fans, tip seals of a labyrinth type have been used to reduce tip air leakage or the flow of air in a gap (on the order of 5 mm) between the shroud and rotor. Ribs have also been used in an effort to reduce this air leakage. A disadvantage of the labyrinth seal is that this seal is difficult to manufacture and that often the axial constraints of the vehicle limit the proper design of the seal. Ribs in the tip region only prevent the swirling component of the flow from causing turbulence by reentering the fan. However, the ribs do not seal the air leakage through the tip gap effectively.
Accordingly, there is a need to provide a seal structure to decrease the gap between the rotor and shroud and to remove the swirling components of flow in the tip region of a fan so as to reduce noise with marginal losses in static efficiency.
An object of the invention is to fulfill the need referred to above. In accordance with the principles of the present invention, this objective is achieved by providing a turbomachine for moving air. The turbomachine includes a shroud disposed about a longitudinal axis and a rotor assembly mounted for rotation about the longitudinal axis. The rotor assembly has a plurality of blades and tips of the blades are coupled to an annular band. The annular band is disposed with respect to the shroud so as to define a gap extending continuously between an outer surface of the annular band and an inner surface of the shroud. A seal structure extends from the inner surface of the shroud and into the gap. The seal structure has a density sufficient to reduce swirl of recirculating airflow and to minimize air leakage across the gap.
In accordance with another aspect of the invention, a method of reducing effects of air flow between a shroud and a rotor assembly is provided. The shroud is disposed about a longitudinal axis and the rotor assembly is mounted for rotation about the longitudinal axis. The rotor assembly has a plurality of blades and tips of the blades are coupled to an annular band. The annular band is disposed with respect to the shroud so as to define a gap extending continuously between an outer surface of the annular band and an inner surface of the shroud. The method includes providing fibers, bristles or filaments extending from the inner surface of the shroud and into the gap to reduce swirl and minimize air leakage across the gap.
Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification.